Communications systems and particularly wireless communications systems have become relatively more complex and have greater system capacities and higher operating frequencies. There are many more variations in such systems and more adaptations of those systems to provide service to ever increasing numbers of users, many with greater bandwidth requirements. Many of these systems now use antenna arrays and smart or adaptive antenna arrays to help satisfy these capacity requirements. For example, adaptive antenna arrays are contemplated for Code Division Multiple Access (CDMA) systems such as CDMA 2000, Wideband CDMA (W-CDMA), Universal Mobile Telecommunications System (UMTS) and 3GPP to name a few.
Antenna arrays allow for antenna gains to be relatively higher in certain directions than in other directions. Smart or adaptive antennas are arranged to adjust or vary the direction of the lobes or beams that form the antenna gain pattern. These beams or relatively higher antenna gains may be adapted or steered to point in different directions. In interference limited systems such as those noted above and most modern systems adaptive antenna arrays can provide dramatic improvements in system capacity—in effect decreasing interference from one user to another. This however presents a problem when it is not known what the direction of arrival may be for a desired signal. A receiver and associated control elements or resources will need to make an initial determination as to whether a desired signal is present in a received signal. This can use a significant amount of signal processing resources and errors in the detection of the desired signal will use more such resources.
The problem can be exacerbated when as is typical the desired signal is arriving via numerous multipaths many with unique directions of arrival and it may be required or desirable to receive, combine and otherwise process several of these multipaths in order to establish and maintain a link with a user via the desired signal. The problem gets even bigger at an uplink receiver for a base station transceiver where the receiver is attempting to establish or provide service for tens or hundreds of users each with an unknown direction of arrival for a plurality of multipaths. As system capacities increase the problem gets larger. Often the function that addresses this problem is referred to as a searcher and known such functions tend to use extensive signal processing resources and also tend to be error prone.
What is needed is a method and apparatus that can efficiently determine whether a received signal includes a desired signal.